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CVE-2026-74434
rxrpc: Don't move a peeked OOB message onto the pending queue
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/rxrpc. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74434 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
rxrpc_recvmsg_oob() takes a received oob message off recvmsg_oobq and, if a response is needed, moves it onto the pending_oobq tree. However, only the unlink from recvmsg_oobq is guarded by MSG_PEEK; the move onto pending_oobq always runs. As a result, reading a challenge with MSG_PEEK leaves the skb on recvmsg_oobq while also adding it to pending_oobq. Since struct sk_buff's rbnode shares storage with its next and prev pointers, rb_insert_color() overwrites the list linkage, and the skb, which holds a single reference, becomes reachable from both queues at once. When the socket is closed both queues are drained in turn. While draining recvmsg_oobq, __skb_unlink() follows the next and prev pointers that rbnode has overwritten and writes to a bad address. Also, as the skb holds a single reference but is freed from each queue, both the skb and the connection reference it holds are released twice. This leads to memory corruption and to a use-after-free caused by the connection refcount underflow. MSG_PEEK does not consume the message from the queue, so only unlink it from recvmsg_oobq and then move it onto pending_oobq or free it when the message is actually consumed.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/rxrpc/recvmsg.c
- What this is
- RXRPC SOCKETS (AF_RXRPC)MAINTAINERS section matched on net/rxrpc/ · linux-afs@lists.infradead.org · Supported
- Kernel module
- rxrpc
Check it on the machine
grep -w CONFIG_AF_RXRPC /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w rxrpcPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_AF_RXRPC
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.63%, higher than 49.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/rxrpc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.40 | 9ada3931beb3 |
| 6.16 | 7.1.5 | 5f470cc88341 |
| 6.16 | 7.2 | 5801cff7d5d7 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A remote RxRPC/AFS peer can deliver CHALLENGE packets over UDP to a victim AF_RXRPC client socket; those packets are queued for recvmsg() handling, so the vulnerable rxrpc_recvmsg_oob() path is reached from network-driven authentication traffic rather than purely local-only APIs.
- AC:LAttack complexity, low
- An attacker who controls both ends of the connection (or a malicious remote server and a userspace client) can reliably queue a CHALLENGE, call recvmsg(MSG_PEEK) with RXRPC_MANAGE_RESPONSE enabled, then close the socket to trigger duplicate queueing and deterministic double-free/UAF during OOB queue purge.
- PR:NPrivileges required, none
- Exploitation requires no privileges on the victim host beyond what any unauthenticated remote RxRPC/AFS server already has to send protocol packets during connection security negotiation; no CAP_NET_ADMIN, root, or namespace-admin capability is needed on the target system.
- UI:NUser interaction, none
- No victim user interaction is required beyond normal automated RxRPC/AFS client operation that receives and processes authentication challenges from a server; the attacker does not need the victim to perform a separate manual action beyond routine client-server communication.
- S:UScope, unchanged
- The corrupted component is kernel RxRPC socket state and the impact is kernel memory corruption and privilege escalation within the same kernel security authority, not a cross-boundary escape such as a VM or sandbox breakout.
- C:HConfidentiality impact, high
- The bug leaves one sk_buff referenced from both recvmsg_oobq and pending_oobq, causing double free and rxrpc_connection refcount underflow; this is a use-after-free/memory-corruption primitive that can expose or read freed kernel heap contents.
- I:HIntegrity impact, high
- rb_insert_color() overwrites sk_buff list linkage shared with rbnode, and socket teardown calls __skb_unlink() on corrupted pointers leading to out-of-bounds writes, enabling control of freed objects and potential arbitrary kernel code execution.
- A:HAvailability impact, high
- Closing the socket drains both OOB queues and reliably triggers invalid pointer writes, skb double-free, and connection refcount underflow, producing kernel oops/panic and complete loss of system availability even without full exploitation.